The present invention relates to a temperature probe for measuring temperature gradients along the length of the probe and, in particular, to a probe for measuring temperatures in a tank of cryogenic liquid.
In cryogenic liquid tanks (for example, propellant tanks for aerospace vehicles), it is important to know the temperature in various levels of the liquid. As the density of the liquid varies with temperature, this information is important to determine such values as the mass of the liquid in the tank.
Propellant tanks are usually more than 5 feet tall and typically in the range of 8 to 100 feet tall. Typically, the measurement of the temperatures in these tanks has been done with temperature sensors mounted on a metallic rake-like structure consisting of vertical and horizontal beams with temperature sensors mounted at various locations on the rake. The vertical beam is typically hard mounted inside the tank from either the lid of the tank or from another structure located inside the tank. The horizontal beams are fastened to the vertical beam.
The rake is usually made from aluminum and is strong enough to support the temperature sensor mounting fixtures, the temperature sensors and the wiring harness. The mounting fixtures are typically constructed of a low conductivity material such as G-10. The wiring harness typically consists of Teflon coated copper wires. Typical temperature sensors include silicon diodes, thermocouples, thermopiles, thermistors, and RTDs.
Each temperature sensor within the tank typically has 2 or 4 wires that must penetrate the tank through multiple pin cryogenically rated electrical feed throughs and associated internal and external multiple pin connectors.
The weight of this rake structure has a significant adverse impact on mission performance and decreases the amount of useful payload on a flight vehicle. In addition, the rake structure is difficult to install in many tanks. Typically the rake must be assembled in sections because the entrances to the tank are too small to allow passage of a pre-assembled rake. Further, the interior geometry of a tank is often less than regular. This makes it difficult or impossible to measure temperatures in many areas of the tank with a rake.
Another disadvantage of a rake temperature probe (besides the large number of parts) is the many solder joints employed to connect the sensors to the wiring harness.
A cryogenic liquid temperature probe includes an elongate first dielectric layer having a first and a second surface, a plurality of temperature sensor units attached to the first layer second surface and spaced along a generally longitudinal direction, and an elongate second dielectric layer having a first and a second surface. The second layer first surface has an elongate conductor thereon for each unit that makes abutting electrical contact with the respective unit. The layers are flexible at room temperature.